摘要:

Bacteria were isolated and characterized from uncolonized soil, nonmycorrhizal and mycorrhizal short roots, and soil-colonizing external mycelium from intactPinus sylvestris-Suillus bovinusandPinus sylvestris-Paxillus involutusmycorrhizospheres developed in microcosms containing dry pine forest humus or nursery peat. Total numbers of colony-forming units (CFU/mg dry weight) in the different locations from all ectomycorrhizospheres indicated an overall bacterial-enrichment gradient towards the roots, whereas sporeformers were more evenly distributed. Fluorescent pseudomonads were commonly isolated from all mycorrhizosphere locations in nursery peat, but they were nearly absent from the forest humus community. In contrast, sporeformers were more abundant at all locations in the latter growth substrate. The bacterial species composition of forest and nursery mycorrhizospheres was clearly divergent when characterized according to their carbon source utilization patterns in Biolog®GN or GP microplates. Factorial-designed ANOVA of a principal component analysis of the carbon source utilization data showed significant differences between isolates from the two soil types and, to a lesser extent, betweenS. bovinusandPaxillus involutusmycorrhizospheres. Bacterial communities from mycorrhizospheres and uncolonized soil were distinguished by their preferential utilization of carbohydrates and organic and amino acids, respectively.Suillus bovinusassociated bacteria appeared to favour mannitol andPaxillus involutusassociated bacteria appeared to favour fructose as carbon sources. This study demonstrates the combined effect of soil type, fungal symbiont, and precise location on bacterial communities associated withPinus sylvestrisectomycorrhizospheres.Key words: Biolog, carbon source utilization, ectomycorrhiza, Scots pine, soil bacteria.

ISSN:0008-4166    

DOI:10.1139/w98-035

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

The fungicidal properties of the synthetic peptide D4E1 were studied with nongerminated and germinating conidia ofAspergillus flavus,Aspergillus fumigatus, Aspergillus niger,Fusarium moniliforme, andFusarium oxysporum. The minimal lethal concentrations (MLC) needed to kill 100% of germinating conidia ofA. fumigatus, A. flavus,andA. nigerwere 12.5, 12.5, and 25 µM, respectively. The MLC value for nongerminated and germinating conidia of bothFusariumspp. was 3.0 µM. Except forA. fumigatus, D4E1 was inactive against the nongerminated conidia of theAspergillusspp. Physicochemical studies showed D4E1 complexed with ergosterol, a sterol present in conidial walls. Cholesterol, present in nongerminated conidia ofF. moniliforme,had a greater affinity for D4E1 than did ergosterol. D4E1 was more resistant to fungal and plant protease degradation than the natural peptide, cecropin A. These in vitro results suggest D4E1 is a candidate for transgenic expression in plants to enhance host resistance to fungal infection.Key words: peptides, fungicidal,Aspergillusspp.,Fusariumspp., sterols.

ISSN:0008-4166    

DOI:10.1139/w98-032

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Siderophores are organic biomolecules synthesized by a wide variety of microbes. The molecules sequester ferric ion from environments where it is present at extremely low concentrations. Siderophores are of consequence with respect to microbial nutrition, pathogenicity, virulence, and microbe-plant interactions. How siderophores are degraded and returned to the carbon and nitrogen cycles is not well understood. The catalytic activity of an enzyme from a bacterium that degrades the siderophore deferrioxamine B has been examined. While the degradation of deferrioxamine B is sensitive to sulfhydryl and metal moiety inhibitors, the data presented is most consistent with the hypothesis that the enzyme uses a hydroxyl moiety (serine peptidase) to catalyze the degradation of deferrioxamine B. If sulfhydryl and metal inhibitors are simultaneously present at concentrations that when alone only partially inhibit the enzyme, the enzyme is unable to catalyze deferrioxamine B dissimilation. Analysis of the inhibitor experiments conducted led to the conclusion that the deferrioxamine B degrading enzyme is a serine-peptidase-like enzyme that needs calcium ions and sulfhydryl groups to be fully activated or stabilized. The knowledge of the catalytic moieties of the enzyme will be exploited to purify the enzyme.Key words: siderophores, deferrioxamine B, siderophore degradation.

ISSN:0008-4166    

DOI:10.1139/w98-031

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

The potential utilization of a plant growth promoting rhizobacterium,Pseudomonassp. strain PsJN, to enhance the resistance of tomato transplants to verticillium wilt was investigated. Plant growth and disease development were tested on the disease-susceptible cultivar Bonny Best afterVerticillium dahliaeinfection of tissue culture plantlets bacterized in vitro (by co-culturing with the bacterium) and seedlings bacterized in vivo (after 3 weeks growth in the greenhouse). Significant differences in both disease suppression and plant growth were obtained between in vitro bacterized and nonbacterized (control) plants. The degree of protection afforded by in vitro bacterization depended on the inoculum density ofV. dahliae; the best and worst protection occurred at the lowest (103conidia ·mL-1) and highest (106conidia ·mL-1) levels, respectively. In contrast, the in vivo bacterized tomatoes did not show plant growth promotion when compared to the nonbacterized control plants. When challenged withVerticillium, significant growth differences between in vivo bacterized plants (26.8% for shoot height) and nonbacterized controls were only seen at the 3rd week after inoculation. Compared with the in vitro inoculation, there was no delay in the verticillium wilt symptom expression, even at the lowest concentration ofV. dahliae, by in vivo PsJN inoculation. These results suggest that endophytic colonization of tomato tissues is required for theVerticillium-resistance responses. Plant growth promotion preceeds the disease-resistance responses and may depend on the colonization thresholds and subsequent sensitization of hosts.Key words:Pseudomonassp., plant growth promoting rhizobacterium,Verticillium dahliae, tomato, colonization, plant growth promotion, disease suppression.

ISSN:0008-4166    

DOI:10.1139/w98-017

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Chloroaliphatics are major components of bleached kraft mill effluents. Gene probes and oligonucleotide primers were developed to monitor kraft pulp mill effluent treatment systems for the presence of key genes (dehalogenases) responsible for the dehalogenation of chloroaliphatic organics. The primers were used for polymerase chain reaction (PCR) analysis of genomic DNA extracted from dehalogenating bacterial isolates and from total community DNA extracted from water and sediments of mill effluent treatment systems. PCR amplification with oligonucleotide primers designed fromdhlB, encoding the haloacid dehalogenase fromXanthobacter autotrophicus, revealed the presence of dehalogenase genes in both aerated lagoons and stabilization basins. Similarly, positive results were obtained withmmoXprimers designed from the soluble methane monooxygenase gene ofMethylococcus capsulatusBath. The haloacetate dehalogenase encoding gene (dehH2) fromMoraxellasp. was typically not detected in mill effluent treatment systems unless the biomass was selectively enriched. DNA sequence analysis of several PCR fragments revealed significant similarity to known dehalogenase and methane monooxygenase genes. The results indicated a broad distribution of known dehalogenation genes and bacteria with chloroorganic-degrading potential in the mill effluent treatment systems.Key words: dehalogenase, gene probes, chloroorganics, PCR, mill effluents.

ISSN:0008-4166    

DOI:10.1139/w98-036

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

The production of the phytotoxins phomalide and sirodesmin PL by virulent isolates ofLeptosphaeria maculans(Desm.) Ces. et de Not. (asexual stagePhoma lingam(Tode ex Fr.) Desm.), the causative agent of blackleg or stem canker disease, was investigated. The effects of temperature, light, age of spores, and calcium ions on the production of phomalide, as well as a correlation between phomalide and sirodesmin PL production, were determined. Finally, the effect of phomalide on fungal spore germination of virulent isolates and isolation of phomalide from blackleg-infected foliar tissue are reported for the first time.Key words:Leptosphaeria maculans,Phoma lingam, phomalide, sirodesmin PL, HPLC analysis.

ISSN:0008-4166    

DOI:10.1139/w98-034

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Defined insertion mutations have been constructed in theRhizobium(Sinorhizobium)meliloti phbCgene, which encodes poly-&bgr;-hydroxybutyrate (PHB) synthase. The locus was isolated and subcloned from a genomic library ofR. melilotiRm1021 by complementation of aphbCmutation ofAlcaligenes eutrophus. PHB production was detected in wild-typeR. melilotiunder nutrient-limited conditions but not in rich medium. No PHB production was detected in theR. melilotiphbCmutants. The DNA sequence of theR. melilotiphbCgene was determined. The deduced polypeptide sequence is homologous to previously identified PhbCs from other bacteria. TheR. melilotiphbClocus maps to pRmeSU47a, the smaller of the two megaplasmids in this strain.Key words:Rhizobium meliloti, PHB, PHA, poly-&bgr;-hydroxybutyrate,phbC.

ISSN:0008-4166    

DOI:10.1139/w98-033

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Western blot analyses using anti-Escherichia coliK-12 &sgr;32antibodies and Southern blot analyses usingrpoHandftsXDNA probes were performed using different enteric bacteria. Results show that the bacterial strains analysed have &sgr;32-like transcription factors andftsXandrpoHhomologs in a similar map position. Although the presence of &sgr;32-like factors seems to be extended to allProteobacteria,rpoHandftsXhomologs seem to be present as neighbors in the genome only in the enteric bacteria.Key words: enteric bacteria, heat shock, &sgr;32,ftsX-rpoH.

ISSN:0008-4166    

DOI:10.1139/w98-041

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Isolates (178) belonging toAspergillussectionsFumigati, Candidi, Clavati, andCircumdatiwere tested for the presence of double-stranded RNA (dsRNA) genomes. Altogether, 5.6% of theAspergillusstrains examined were infected with dsRNAs. dsRNA segments indicative of mycovirus infection were observed for the first time inNeosartorya hiratsukae, Neosartorya quadricincta,Petromyces alliaceus,andAspergillus clavatusstrains. Correlation was not observed between ochratoxin production and dsRNA content of the strains. This is the first report on the detection of naturally occurring dsRNAs inAspergillusspecies that are able to reproduce sexually. The detection of dsRNA in sexual aspergilli gave us a chance to examine the transmission of these segments through ascospores. ANeosartorya hiratsukaestrain transmitted the dsRNAs efficiently through sexual spores, while the stromata embedding the asci inPetromyces alliaceusdid not transmit one of the dsRNA segments. The 0.6-kb dsRNA segment that was present in the single-stromatal cultures was found to be located in the mitochondrial fraction of this strain. This observation indicates that some mechanisms exist in aspergilli to exclude cytoplasmically located dsRNA molecules from stromatal structures.Key words:Aspergillus,double-stranded RNA, mycovirus,Petromyces,Neosartorya.

ISSN:0008-4166    

DOI:10.1139/w98-038

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Cell wall chitin was determined in the mycelia of the brown rot fungusNeolentinus lepideus(Lentinus lepideus) and an isolate of the soft rot fungusPhialophorasp. to study the correlation to mycelial dry mass. The fungi were incubated as liquid cultures for three incubation periods at three temperatures in six nutrient media with varying levels and combinations of carbon and nitrogen. The glucosamine yield was found to be maximized by hydrolysis at 90°C for 48 h. The chitin content in the studied fungi varied from 8.3 to 39.8 &mgr;g.mg-1forN. lepideusand 7.7 to 46 &mgr;g.mg-1for thePhialophoraisolate. The chitin concentration was remarkably constant, about 10 &mgr;g.mg-1, in mycelia growing on the low nitrogen malt extract medium. An experiment with wood blocks indicated that chitin may be a good marker for total fungal biomass production, including living and dead mycelia, in early stages of wood decay (dry weight loss <6%). At higher dry weight losses, the chitin content reaches a plateau or decreases despite continuing degradation as determined by the dry weight loss. The chitin content of visible mycelia growing on wood was determined for both fungi and found to be 19.1 and 12.9 &mgr;g.mg-1forN. lepideusand thePhialophoraisolate, respectively.Key words: chitin, wood-decay fungi, utility poles, brown rot, soft rot, glucosamine, colorimetry.

ISSN:0008-4166    

DOI:10.1139/w98-039

出版商:NRC Research Press    

年代:1998

数据来源: NRC